Mesh is almost entirely black in rendered mode
Your model is quite a mess.

Your sunlight doesn't seems to be emitting any light - Create a native Cycles Sun or give the current one a proper shader node tree.

Your model is full of custom normals which are known to cause shading trouble - Clear your custom normals

Some textures seem to not be picking up proper UV channel - Add an explicit Texture Coordinate node with UV coordinates to your textures.

Most of your geometry seems to have Inverted Normals - Recalculate normals and make sure they are pointing outwards